1. Field of the Invention
The present invention relates to a holographic combiner designed to be mounted on aircraft.
The essential role of such combiners is that of presenting, before a pilot's eyes, light images that are collimated at infinity in being superimposed on the external scene.
These images are produced in relief by using the interferences between two laser beams, according to the known principle of holography.
The images come from a projector positioned upline with respect to the combiner, the relative position of this projector with respect to the holographic mirror, when it is operational, being fixed.
2. Description of the Prior Art
Such combiners are held and positioned by means of a mechanical device, and are generally mounted on the ceiling in the cockpit of the aircraft, the mounting being done in a retractable way.
Indeed, since the system for the collimation of holographic images is used only during certain stages of flight, the combiner should be capable of being stowed away, for the rest of the time, in a zone that spoils the external field of vision of the pilot to the minimum extent.
However, at the present time, the mechanical holding and positioning devices cannot be used for the total retraction of the combiners, and a part of the mechanism remains visible in the field of vision of the pilot, even when it is stowed away.
Indeed, these known devices are constituted by two arms positioned on either side of the holographic mirror, and are connected to an upper fixed part of the ceiling of the cockpit.
It is important to note that, in this type of known combiner, the holographic mirror is fixedly joined to the arm that supports it, the drawback of which is that it constitutes an assembly with a substantial space requirement, which is a penalizing factor when the assembly is stowed away, whence the difficulty of complete retraction. Furthermore, the length that is necessary for this succession of elements may force the pilot to make a backward movement to allow them to pass when the combiner is being stowed away or being put into operational position. Such a movement may be detrimental to the piloting of the aircraft.
Furthermore, lateral handles are provided on either side of the holographic mirror in order to constitute grips that are necessary for manoeuvring the apparatus without touching the holographic mirror.
It will easily be seen that such an apparatus is detrimental to clear visibility and adds to the difficulties of full retraction of the combiner.
Indeed, the greater the number of components of the combiner, the greater is the extent to which the field of vision is masked in an operational position as well as a stowed position, in the latter case because of the very difficulty of achieving complete retraction.